The invention pertains to a method of reducing organic halides and more particularly to the use of a nickel-triaryl phosphine, halide catalyst in conjunction with reducing means capable of maintaining the nickel in a zero valent state.
The hydrogenolysis of carbon-halogen bonds has been effected in the past by hydrogen in the presence of nickel or palladium (F. W. Neuman, N. B. Sommer, C. E. Kaslow, and R. L. Shriner, Org. Syn., Coll. Vol., 3, 519, 1955; H. Kammerer, L. Horner, and H. Beck, Chem. Ber., 91, 1376, 1958; C. K. Alden and D. I. Davies, J. Chem. Soc., C, 700, 1968; M. G. Reinecke, J. Org. Chem., 29, 299; D. A. Denton, F. J. McQuillin, and P. L. Simpson, J. Chem. Soc., 5535, 1964), and by metal hydrides (R. O. Hutchins, D. Hoke, J. Keogh, and D. Koharski, Tet Lett., 3495, 1969; H. M. Bell, C. W. Vanderslice, and A. Spehar, Jr. Org. Chem., 34, 3923, 1969; E. L. Eliel, J. Am. Chem Soc., 71, 3970, 1949; G. J. Karabatsos and R. L. Shone, Jr. Org. Chem., 33, 619, 1968; R. A. Egli, Helv. Chim. Aceta, 51, 2090, 1968). The metal hydride technique suffers from the disadvantage that metal hydrides are not very selective and will reduce a large number of other functional groups in the substrates as well. Carbon-halogen bonds may also be reductively cleaved by reaction with metals in protonic solvents (P. A. Levene, Org. Syn., Coll. Vol. 2, 320, 1943; S. Gronowitz and T. Raznekiewicz, Org. Syn., 44, 9, 1964; P. G. Gassman and J. L. Marshall, Org. Syn., 48, 68, 1968; D. Bryce-Smith and B. J. Wakefield, Org. Syn., 47, 103, 1967; C. F. Wilcox, Jr., and F. G. Zajacek, Jr. Org. Chem., 29, 2209, 1964; C. E. Moppett and J. K. Sutherland, and J. Chem. Soc., C, 3040, 1968), by treatment with chromium (II) salts (D. M. Singleton and J. K. Kochi, J. Am. Chem. Soc., 89, 6547, 1967; 90, 1582, 1968; J. K. Kochi, D. M. Singleton, and L. J. Andrews, Tetrahedron, 24, 3503, 1968; R. E. Erickson and R. K. Holmquist, Tet. Lett., 4209, 1969; J. K. Kochi and P. E. Macadlo, J. Am. Chem. Soc., 88, 4094, 1966), and by electrolytic methods (A. J. Fry, M. A. Mitnick, and R. G. Reed, J. Org. Chem., 35, 1232, 1979; J. L. Webb, C. K. Mann, and H. M. Walborsky, J. Am. Chem Soc., 92, 2042, 1970; F. H. Covitz, J. Am. Soc., 89, 5403, 1967; R. E. Erickson, R. Ammino, M. D. Scanlon, and G. Zon, J. Am. Chem. Soc., 91, 1767, 1969; A. J. Fry and R. H. Moore, J. Org. Chem., 33, 1283, 1968).
Although zinc in acidic media has been used alone to reduce organic halides, its use is usually limited to iodides and bromides. Chlorides such as chlorobenzene are not reduced by zinc in this system.
Nickel has been used previously to catalytically reduce alkyl and aryl halides when used in combination with either sodium borohydride (S.-T. Lin and J. A. Roth, J. Org. Chem., 44, 309, 1979; W. H. Denis, Jr., W. J. Cooper, Ventron Alembic, 9, 4, 1977) or lithium aluminum hydride (E. C. Ashby and J. J. Lin, J. Org. Chem., 43, 1263, 1978), but the procedures were not selective. Functional groups such as carbonyls, nitriles, and the like, did not survive the reaction conditions.
Reduction of aryl halides by zero-valent nickel compounds has been observed before (M. F. Semmelhack, P. M. Helquist, and L. D. Jones, J. Am. Chem. Soc., 93, 5908, 1971; L. Cassar and M. Foa, J. Organoment Chem., 51, 381, 1973). However, none of these prior art reductions with zero-valent nickel were carried out in a manner where the nickel was used in catalytic amounts.
It is therefore an object of this invention to provide a method for reducing aryl halides in a selective manner which does not reduce other functional groups in the substrate compound.
Another object of this invention is the provide a method of reducing aryl halides using zero-valent nickel in catalytic amounts.
A further object of this invention is to provide a method of detoxifying polychlorinated biphenyls by reducing them to biphenyl.
Other objects of this invention will become apparent to those skilled in the art upon a further reading of the specification.